LASER TORCH BASED VOICE TRANSMITTER AND RECEIVER

•This product can be used for communication between neighbors or some in nearby buildings.

Block Diagram

The block diagram describes main parts of the transmitter and receiver.

Transmitter

[Microphone] --- [Audio signal pre-amplifier] --- [Modulating transistor] --- [Laser torch]

The voice signal from any source is picked up using a condenser mic. This signal ia passed through an audio signal pre-amplifier, and is given to an op-amp stage. The output of op-amp stage is given to a modulating transistor section. The laser torch radiates light into the air.

Reciever

[Photo transistor] --- [Two stage pre-amplifier] --- [Audio power amplifier] --- [Loud speaker]

 The light from the laser torch is made to fall on a photo transistor. Then the signal is amplified to sufficient level using a two stage pre-amplifier. It is then given to an audio power amplifier. Finally the voice is heard as the output from the speaker.

Circuit Diagram

Transmitter

Reciever

Working

   The transmitter circuit comprises condenser microphone tranasistor amplifier BC548(T1) followed by an op- amp stage build around 741 IC (IC1). The gain of the operational amplifier (op-amp) can be controlled with the help of one mega ohm (1M Ω) potentiometer VR1. The AF output from IC1 is coupled to the base of the transistor BD139 (T2) which in turn, modulates the laser beam. The transmitter uses 9V power supply. The receiver circuit uses an npn photo transistor as the light sensor. A two stage transistor pre-amplifier and LM386 based audio power amplifier is used to amplify the received signal. To avoid 50 Hz human noise in the speaker keep the photo transistor away.

  The components are easily available for this and it is a simpler and efficient circuit. It has low maintenance cost and high data rate. The laser transmission is very secure because it has a narrow beam. There are no recurring line costs. It has narrow beam divergence.

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